Hi Ali, I just googled the song and the lyrics are apparently: 'Sometimes the only pay off for having any faith, Is when it's tested again and again everyday,' A 'pay off' is the what you get from something, so this is saying that the only positive result from having faith is that it is tested every day. With 'blackout curtains' - these were very thick curtains used in World War 2 to block out the lights from inside houses, so that they wouldn't be seen by enemy bombers at night and targeted. I guess in the song this could be used figuratively, so the person is putting up emotional walls or not showing their true selves, or something like that. Hope this helps.

I should refine the first example sentence is the only pay off(instead of we only pay off) thank you all in advance